Work machines such as, for example, excavators, loaders, dozers, motor graders, and other types of heavy machinery use one or more hydraulic actuators to accomplish a variety of tasks. These actuators are fluidly connected to a pump on the work machine that provides pressurized fluid to chambers within the actuators. An electro-hydraulic valve arrangement is typically fluidly connected between the pump and the actuators to control a flow rate of pressurized fluid to and from the chambers of the actuators. The fluid flow rate into and out of the chambers of the actuators directly relates to a speed of the actuators.
Work machine hydraulic circuits that fluidly connect multiple actuators to a common pump may experience undesirable pressure fluctuations within the circuits during operation of the actuators. In particular, the pressure of a fluid supplied to one actuator may undesirably fluctuate in response to a different actuator consuming fluid from or expelling fluid to the same hydraulic circuit. These pressure fluctuations may cause inconsistent and/or unexpected actuator movements when the electro-hydraulic valve arrangement is area-controlled. In particular, to move an actuator at a desired speed, an element of the electro-hydraulic valve arrangement may be moved to open a fluid passageway to a particular opening area. The particular opening area is based upon an assumed supplied pressure that corresponds to a desired flow rate and resulting actuator speed. When the pressure of the fluid supplied to the electro-hydraulic valve arrangement deviates from the assumed pressure, the flow rate and resulting speed of the actuator proportionally deviate from the desired flow rate and speed.
One method of improving control over the flow rate of fluid supplied to an actuator is described in U.S. Pat. No. 5,878,647 (the '647 patent) issued to Wilke et al. on Mar. 9, 1999. The '647 patent describes a hydraulic circuit having two supply valves, a variable displacement pump, and a hydraulic actuator. The supply valves connect the variable displacement pump to either a head-end or a rod-end of the hydraulic actuator to cause movement of the hydraulic actuator. Each of these supply valves contains a pressure compensating mechanism that senses the pressure at the outlet of the supply valves and provides the greatest of those pressures to a control input of the variable displacement pump to affect operation of the variable displacement pump. The operation of the variable displacement pump may be affected to cause the pressure drop across each of the supply valves to be approximately constant, thereby bringing the supplied pressure and resulting flow rate of fluid through each of the solenoid valves closer to the assumed pressure and desired flow rate.
Although the pressure compensating mechanisms described in the '647 patent may reduce pressure fluctuations within the hydraulic circuit, they may be slow to respond, expensive, and increase the unreliability of the hydraulic circuit. Specifically, the pressure compensating mechanisms of the '647 act to affect the pressure of the fluid directed through the supply valves only after sensing an undesired pressure drop across the supply valves. In addition, even after the pressure compensating mechanisms have changed pump performance, the effects of the change may not be realized immediately. By the time the undesired pressure drop has been adjusted to match the assumed pressure drop, the flow rate of fluid supplied to the actuator may already have deviated from the desired flow rate for a substantial period of time. In addition, the added components of the pressure compensating mechanisms may increase the cost and unreliability of the hydraulic circuit.
The disclosed metering valve is directed to overcoming one or more of the problems set forth above.